1. Field of the Invention
This invention relates to a lens barrel, and particularly to a lens barrel which has the auto focusing mode and the manual focusing mode and in the changeover between the two focusing modes may be effected very quickly and easily to thereby improve operability and the responsiveness of the focusing operation in the auto focusing mode is improved.
2. Related Background Art
Recently, almost all of camera systems such as still cameras or video cameras have the auto focusing function and the manual focusing function, and are designed such that a photogapher can selectively use the auto focusing (hereinafter simply referred to as AF) mode and the manual focusing (hereinafter simply referred to as MF) mode by changeover as required. In the lens barrel of such a camera in which the AF mode and the MF mode can be changed over, design is made such that during the AF mode, a lens is driven by a motor or the like and during the MF mode, the motor is stopped and a manually operated ring such as a distance ring is manually turned to thereby axially move the lens. Also, as a changeover mechanism for the AF mode and the MF mode, a clutch mechanism is provided in a driving system for a focusing lens and when changeover is to be done from the AF mode to the MF mode, a driving system for AF may be interrupted by this clutch mechanism and the operatively associated member of the focusing lens may be directly manually operated to drive the focusing lens.
As a lens barrel of this type, there is proposed one described in Japanese Patent Application Laid-Open No. 4-218006. In this lens barrel, which has a focusing optical system, a holding cylinder for holding the focusing optical system and moving it in the direction of the optical axis thereof to thereby effect focusing, a cam cylinder rotatable about the optical axis and moving the holding cylinder by said rotation, manually operated means rotatable by a manual operation and rotating the cam cylinder by said rotation, AF driving means, automatically operated means driven by the AF driving means and rotating the cam cylinder by said driving, and clutch means displaceable to a first position and a second position, and when in the first position, connecting the cam cylinder and the manually operated means together, and when in the second position, connecting the cam cylinder and the automatically operated means together, a motor is used as a drive force source for driving a device for effecting the changeover between an AF device and an MF device. When a photographer gives a predetermined electrical signal from outside for the purpose of changeover, the electrical signal is transmitted to the motor, which is thus rotated, whereby the changeover from the AF device to the MF device or from the MF device to the AF device is effected depending on the forward or reverse direction of the rotation of the motor. Thereby, it is made possible to effect the changeover quickly by small consumption of electric power.
However, in the lens barrel proposed in the aforementioned Japanese Patent Application Laid-Open No. 4-218006, the whole or a part of the changeover mechanism for the AF mode and the MF mode is carried out on a cam cylinder and therefore, the load torque and moment of inertia during AF servo driving become great. This has sometimes given rise to the problem that the converging time of AF servo becomes long and the performance of the foreseen driving of a moving object becomes bad or servo accuracy is aggravated to reduce the in-focus accuracy during photographing with a result that focusing becomes bad.